In the semiconductor processing industry there continues to be a need to pack an increasing number of electronic devices, such as transistors and capacitors, onto a single integrated circuit chip. This continuously increasing level of integration is accomplished in large part by decreasing the minimum feature sizes of the devices. Feature alignment from one semiconductor level to the next is of critical importance, particularly relating to the alignment of contact holes with the underlying structures with which they are to connect, such as active areas. Device miniaturization complicates the process of forming interconnect structures because in order to maintain sufficient electrical communication, the interconnect structure must be formed in exact alignment with an underlying active region. At the same time, the area of the interconnect structure interfacing with the active area must be maximized. Thus, as device sizes shrink there is less room for misalignment errors of the interconnect structure.
As minimum feature sizes decrease, it becomes increasingly more difficult to control the photolithographic alignment within design tolerances and to control the critical dimensions. Misalignment of the photoresist mask can inadvertently result in etching underlying insulating layers causing electrical shorts between the various electrically conducting elements.
The prior art has been successful at developing etching processes that exhibit significantly higher etch rates for insulating oxides than nitrides. That is, these etching processes are highly selective to nitrides. One approach to improving nitride selectivity, involves the use of certain fluorocarbon gases in the etching gas (that is, the etchant). The fluorocarbons known in the art for nitride selectivity have two or more carbon atoms and no hydrogen atoms. Accordingly, these nitride-selective fluorocarbons will be referred to in the present specification as C2+F gases or C2+F chemistry. C2+F gases include C3F6, C3F8, C4F6, C4F8, and C5F8, for example.